Natural alignment knee instruments

ABSTRACT

A method for aligning an orthopedic implant in a joint replacement includes determining the bone and cartilage deficiency from an undegenerated state caused by wear of a joint. Then a resection of a bone in the joint is made based on the deficiency of bone and cartilage from the undegenerated state and the size of a joint implant so as to locate the joint surface of the implant in the undegenerated cartilage location. The condylar wear from the undegenerated states may be assessed at a distal and posterior location on each of a medial and a lateral femoral condyle. A distal cut is made on the femur at a location adjusting for the condylar wear from the undegenerated state. The distal cut varus-valgus angle is oriented parallel to a plane across the distal femur after adjusting for wear in the distal location on the medial and lateral condyle.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 13/113,414, filed May 23, 2011, which claims the benefit of thefiling date of U.S. Provisional Patent Application No. 61/347,045, filedMay 21, 2010, the disclosures of which are hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

Over time and through repeated use, bones and joints can become damagedor worn. For example, repetitive strain on bones and joints (e.g.,through athletic activity), traumatic events, and certain diseases(e.g., arthritis) can cause cartilage in joint areas, which normallyprovides a cushioning effect, to wear down. When the cartilage wearsdown, fluid can accumulate in the joint areas, resulting in pain,stiffness, and decreased mobility.

Arthroplasty procedures can be used to repair damaged joints. During atypical arthroplasty procedure, an arthritic or otherwise dysfunctionaljoint can be remodeled or realigned, or an implant can be implanted intothe damaged region. Arthroplasty procedures may take place in any of anumber of different regions of the body, such as a knee, a hip, ashoulder, or an elbow.

One type of arthroplasty procedure is a total knee arthroplasty (“TKA”),in which a damaged knee joint is replaced with prosthetic implants. Theknee joint may have been damaged by, for example, arthritis (e.g.,severe osteoarthritis or degenerative arthritis), trauma, or a raredestructive joint disease. During a TKA procedure, a damaged portion inthe distal region of the femur may be removed and replaced with a metalor ceramic femoral implant, and a damaged portion in the proximal regionof the tibia may be removed and replaced with a tibial implant having anultra high molecular weight polyethylene (UHMWPE) bearing. In some TKAprocedures, a UHMWPE bearing may also be implanted on the posteriorsurface of the patella, depending on the condition of the patella.

Implants that are implanted into a damaged region may provide supportand structure to the damaged region, and help to restore the damagedregion, thereby enhancing its functionality. Prior to implantation of animplant in a damaged region, the damaged region may be prepared toreceive the implant. For example, in a knee arthroplasty procedure, oneor more of the bones in the knee area, such as the femur and/or thetibia, may be prepared (e.g., cut, drilled, milled, reamed), to provideone or more surfaces that can align with the implant and therebyaccommodate the implant.

Accuracy in implant alignment is an important factor in the success of aTKA procedure. A one- to two-millimeter translational misalignment, or aone- to two-degree rotational misalignment, may result in imbalancedligaments, and may thereby significantly affect the outcome of the TKAprocedure. For example, implant misalignment may result in intolerablepost-surgery pain, and also may prevent the patient from having full legextension and stable leg flexion.

To achieve accurate implant alignment, prior to preparation (e.g.,cutting, drilling, reaming, and/or milling) of a bone, it is importantto correctly determine the location at which the preparation will takeplace and how the bone resections will be oriented. In most surgicalmethods, an arthroplasty jig is used to accurately position and orientbone resection instrumentation, such as a cutting, drilling, reaming, ormilling instrument on bone. The arthroplasty jig may, for example,include one or more apertures and/or slots that are configured to acceptand guide such a bone resection instrument.

Femoral and tibial preparation instruments for Total Knee Arthroplasty(TKA) are known in the art and conventionally reference theintermedullary (IM) canal or extramedullary (EM) features such as thelong axis of the femur and tibia. As such, standard surgical techniquesare designed to align the bone preparation to the mechanical axis oranatomic axis of the patient. Typical knee instruments are shown in U.S.Pat. Nos. 4,487,203, 5,037,423 and 6,558,391.

Preoperative assessment of bone loss is advantageous for prosthesisdesign, for example, to reduce the likelihood of prosthesis looseningand to provide a more reliable bone restoration method for preoperativeimplant design, thereby improving the success rate for such proceduressuch as total knee arthroplasty (TKA) and partial knee arthroplasty(e.g., a unicompartment knee arthroplasty) and providing apatient-specific bone restoration method to fit an individual patient'sknee features.

The current available joint reconstruction and replacement surgeries,including knee, ankle, hip, shoulder or elbow arthroplasty, are mainlybased on standard guidelines and methods for acceptable performance.Taking this into account, the positioning and orientation of thearthroplasty work on a joint is based on standard values for orientationrelative to the biomechanical axes, such as flexion/extension,varus/valgus, and range of motion.

One of the surgical goals of joint replacement/reconstruction should beto achieve a certain alignment relative to a load axes. However, theconventional standards are based on static load analysis and thereforemay not be able to provide an optimal joint functionality for adoptingindividual knee features of OA patients. The methods disclosed hereinprovide a natural approach for bone restoration, properly balancing theunconstrained joint and ligaments surrounding the joint, and resultingin a placement of a prosthetic implant that generally restores thepatient's knee to a generally pre-degenerated state.

In one embodiment, the result of the bone restoration process disclosedherein is a TKA or partial knee arthroplasty procedure that generallyreturns the knee to its pre-degenerated state whether thatpre-degenerated state is naturally varus, valgus or neutral. In otherwords, if the patient's knee was naturally varus, valgus or neutralprior to degenerating, the surgical procedure will result in a knee thatis generally restored to that specific natural pre-degeneratedalignment, as opposed to simply making the knee have an alignment thatcorresponds to the mechanical axis, as is the common focus and result ofmost, if not all, arthroplasty procedures known in the art.

While success has been reported for traditional instruments andmechanical alignment techniques, alternative alignment methods such asanatomic or “natural” alignment are being developed. The anatomicalignment method references a “natural” or pre-arthritic state of aspecific patient's anatomy. These alternative methods require newinstruments designed for referencing resected and un-resected aspects ofthe femur and tibia. Further, these new instruments will allow forpreparation and final implant position in a pre-arthritic and anatomicorientation. The following disclosure describes various instrumentembodiments designed to reference resected and un-resected aspects offemoral and tibial bone and to allow for alignment of bone preparationto an anatomic orientation.

BRIEF SUMMARY OF THE INVENTION

The goal of the present invention is to provide a method andinstrumentation directed toward placing a total knee implant in aposition which replicates the patient's pre-arthritic alignment. Thisphilosophy is discussed in U.S. Patent Publication No. 2009/0270868, thedisclosure of which is incorporated herein by reference. This referenceteaches the use of patient specific cutting guides. The presentinvention utilizes modified conventional instruments to achieve the sameresult. Alternately the same instrumentation can be used in traditionalmethods such as mechanical axis alignment. One aspect of the inventionincludes providing an anatomic distal femoral resection guide alignmentassembly with the ability to adjustably reference the unresected portionof the distal femur when setting the distal femoral resection guidelevel and varus-valgus orientation. Another aspect provides an alternateembodiment of an anatomic distal femoral resection guide alignmentassembly that allows for both reference to the unresected portion of thedistal femur and adjustable reference to the anterior cortex of thefemoral shaft. Another aspect of the invention is the insertion of anextramedullary rod in the distal femoral cutting block to assist inorienting the flexion/extension angle of the distal femoral resectionguide with respect to the anterior thigh and femur. Another aspect ofthe insertion is the provision of an anterior/posterior (AP) sizer withinsertable variable feet which are inserted to compensate for femoralposterior wear. A posterior referencing guide can be provided withvariable feet and/or shoes of varying thickness that can be placed onthe feet to set the AP and internal/external rotation of the femoralimplant. The feet may be rounded in the sagittal plane to better fit thetibial geometry. The AP sizer may be provided with variable thicknessboots which are inserted to compensate for femoral posterior wear.

An additional aspect of the invention is the provision of a femoralreferencing tibial resection alignment system that is designed to allowfor reference of the prepared distal femoral bone and, through the useof femoral condyle spacing elements, to also reference the unresectedtibial surface. Further, this system allows for visualization of ajoint-line in a pre-arthritic or anatomic state. Specifically, thegeometry is an offset of the articulating surface of the femoralcomponent. Peg shape is such that it does not destroy the full diameterof the hole to gain fixation during instrument use but does not ruin thefull hole for implant preparation. Yet an additional aspect of theinvention is the provision of an adjustable slope tibial resection guidewith a conical hole that allows for degrees of tibial slopeadjustability with a single fixation pin placement. A tibial cuttingguide assembly that references the prepared tibial bone and hasreferencing members that allow for correction/refinement of the tibialcut. Refinements may include tibial slope, varus alignment, valgusalignment or any combination of those mentioned. The tibial guide hasmarkings which indicate the implant size for proper positioning of theguide.

Another aspect of the invention is a method for aligning an orthopedicimplant in a joint replacement which includes determining the bone andcartilage deficiency from an undegenerated state caused by wear of ajoint. A resection of a bone is made in the joint based on thedeficiency of bone and cartilage from the undegenerated state and thesize of a joint implant. The resection is located to place the jointsurface of the implant in the undegenerated cartilage location. If thejoint is a knee joint the femoral condylar wear from the undegeneratedstate is assessed at a distal and posterior location on each of a medialand a lateral femoral condyles. The distal cut is then made on the femuradjusting for the condylar wear from the undegenerated state. Thefemoral distal cut varus-valgus angle is oriented parallel to the distalfemur after adjusting for wear in the distal location on the medial andlateral condyle. Thus, when implanted, the joint very closelyapproximates the patient's undegenerated knee, and the transverse axisin the femoral implant is naturally aligned with the transverse axis inthe femur about which the tibia flexes and extends on the femur.

Another aspect of the invention is a method for aligning an orthopedicimplant in a joint replacement including determining the bone andcartilage deficiency from an undegenerated state caused by wear of ajoint. A resection of a bone in the joint is based on the deficiency ofbone and cartilage from the undegenerated state and the size of a jointimplant so as to locate the joint surface of the implant in theundegenerated cartilage location. The method includes assessing thecondylar wear from the undegenerated states at a distal and posteriorlocation on each of a medial and a lateral femoral condyle. The distalcut is made on the femur at a location adjusting for the condylar wearfrom the undegenerated state. The distal cut varus-valgus angle isoriented parallel to a plane across the distal femur after adjusting forwear in the distal location on the medial and lateral condyle. Anotheraspect of the invention is a resection guide for resecting a proximaltibia which guide references a resected distal femoral surface andincludes a tibial condylar member having a body with a proximal surfacefor contacting a resected planar surface of a distal femur and distalsurface. A plurality of modular distal spacer elements are providedwhich include coupling elements for attaching the spacer elements to thedistal surface of the body. A tibial resection guide is coupled to thebody of the trial condylar member and is movable with respect thereto ina proximal-distal direction and rotatable with respect to the body abouta medial-lateral parallel to the resected planar surface of the femur.The tibial references guide may be provided with a shoe or spacer on aposterior condyle reference portion to adjust for the thickness ofcartilage wear.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of the anatomic distalfemoral resection guide alignment assembly of the present invention;

FIG. 2 is a view of the anterior facing surface of a distal femoralreference housing which forms part of the resection guide of FIG. 1;

FIG. 3 is a view of the distal facing surface of the distal femoralreference housing of FIG. 2;

FIG. 4 is a view of the distal facing end of an AP/internal-externalpositioner assembly;

FIG. 5 is a view of the medial facing side of the AP internal-externalpositioner assembly of FIG. 4;

FIG. 6 a is a side view of a posterior referencing foot of the assemblyof FIG. 5;

FIG. 6 b is a top view of the posterior referencing feet assembly ofFIG. 6 a;

FIG. 6C is a rear view of the posterior referencing feet assembly ofFIG. 6 a;

FIG. 7 is a view of the distal facing surface of the AP/IE positionerblock of FIG. 4;

FIG. 8 is a perspective view of an alternate embodiment of the anatomicdistal femoral resection guide alignment assembly;

FIG. 9 is a perspective view of one embodiment of an AP sizer assembly;

FIG. 10 is a perspective view of an alternate embodiment of an AP sizerassembly;

FIG. 11 is a perspective view of yet another embodiment of an AP sizerassembly;

FIG. 12 is a perspective view of a femoral referencing tibial resectionassembly;

FIG. 13 is view of the proximal facing surface of a femoral referencingtemplate;

FIG. 14 is a view of the medial facing surface of the femoralreferencing template of FIG. 13;

FIG. 15 is a view of the medial facing surface of the proximal rod ofthe tibial resection assembly of FIG. 12;

FIG. 16 is a view of the anterior facing surface of an adjustable slopetibial resection guide of the assembly of FIG. 12;

FIG. 17 is a cross sectional view of the adjustable slope tibialresection guide along lines B-B of FIG. 16;

FIG. 18 is a cross sectional view of a bore through the adjustable slopetibial resection guide of FIGS. 16 and 17 with a pin extending throughthe bore;

FIG. 19 is a view of the distal facing surface of a femoral spacer;

FIG. 20 is a view of the medial facing surface of the femoral spacer ofFIG. 19;

FIG. 21 is a perspective view of a tibial clean-up resection guideassembly;

FIG. 22 is a view of the proximal facing surface of the tibial bonereference block removed from the assembly of FIG. 21;

FIG. 23 is a view of the anterior facing surface of the tibial bonereference block of FIG. 22;

FIG. 24 is a view of the medial facing surface of the tibial bonereference block of FIG. 22;

FIG. 25 is an alternate anatomic distal femoral resection guide similarto FIG. 1; and

FIG. 26 is an alternate anatomic distal femoral alignment assemblysimilar to FIG. 8.

DETAILED DESCRIPTION

As used herein, the term “distal” means more distant from the heart andthe term “proximal” means closest to the heart. The term “inferior”means toward the feet and the term “superior” means towards the head.The term “anterior” means towards the front part of the body or the faceand the term “posterior” means towards the back of the body. The term“medial” means toward the midline of the body and the term “lateral”means away from the midline of the body.

Referring to the drawings, FIG. 1 illustrates a first embodiment of ananatomic distal femoral resection guide alignment assembly generallydenoted as 10 which consists of a distal femoral resection guide 11 formaking a distal femur planar cut, an adjustment housing 12, an AP tower13 moveable in an AP direction and a distal femoral referencing housing14 having adjustable pads 22 a. The distal resection guide 11 includes acutting surface 15 for guiding a saw blade, an aperture 16 forattachment to a standard navigation tracker (not shown), pin holes 17for inserting fixation pins to an anterior surface of the femur and aconnector 18 at which the adjustment housing 12 may be removablyconnected from resection guide 11. Connector 18 includes a shaft 18 amounted on resection guide 11 which shaft is slidably mounted in housing12 and can be adjusted with respect thereto to locate the distal cut.

The adjustment housing 12 may be removably or permanently connected tothe AP tower 13. As shown, the housing 12 is bolted onto tower 13 bybolts or screws 20 a. Further, the adjustment housing 12 may containadjustment mechanisms such as rack 20 and pinion 19 that allow forinteroperative adjustment of shaft 18 a in the proximal/distaldirection. AP tower 13 is preferably removably attached to distalfemoral reference housing 14 via a post 104 slidably mounted in track105 (FIG. 2). The AP tower 13 is designed to allow movement in theanterior to posterior direction and can be locked in place with alocking mechanism or locking screw 21.

The distal femoral referencing housing 14 contains two adjustablethreaded elements 22 that adjust pads 22 a which contact the distalfemur and may be used to reference aspects of the distal femoral surfaceprior to resection. The pads 22 a may contain spikes or other features(not shown) for fixation to the surface of the distal femur. The pads 22a allow for varus/valgus adjustment of the system by turning elements 22which are preferably threaded into block 14 and any adjustments may bevisualized by markings 23 on elements 22.

FIGS. 2-3 show further aspects of the distal femoral referencing housing14. FIG. 2 shows track 102 for slidably receiving post 104 of AP tower13. FIG. 3 shows a pair of threaded holes 106 and a pair of non-threadedbores 53 a and 53 b for bone pins which may be inserted into the femur.Also shown is threaded bore 21 a which accommodates locking screw 21.

The method of use for the anatomic distal femoral resection guidealignment assembly 10 illustrated in FIGS. 1-3 will now be described.The proximal surface of the distal femoral referencing housing 14contacts the unresected distal femoral surface. Here, the distal femoralsurface contains cartilage which may be healthy, damaged, ornon-existent depending on the progression of degeneration. The cartilagemay also vary from the left and right condyles. The surgeon uses theadjustable pads 22 a to compensate for any distal femoral cartilage wearwhich may range from 1-3 mm, for example. The surgeon may determine thisby measuring a healthy condyle on the same or opposite knee. Once thesurgeon has used the adjustable pads 22 a to compensate for thecartilage degeneration on the distal femoral surface, the appropriatelevel of distal femoral resection can be adjustably set followed bypinning the distal resection guide 11 to the anterior aspect of thefemoral bone via holes 17. The connector 18 is then uncoupled so a sawmay be used to resect the distal femur.

FIGS. 4-5 illustrate an AP positioner assembly 40 which includes ahandle 41, positioner body 42 and a pair of posterior referencing feet43. Handle 41 consists of a grip portion 44 with a neck 44 a connectedto a body portion 45 which can be removably attached to a distal surface47 of the positioner body 42 by means of a locking mechanism such as athreaded knob 46. The positioner body 42 has, with respect to the femur,a flat distally facing surface 47 and a proximally facing surface 48,attachment slots 49 a and 49 b which extend from surface 47 to 48 andremovably attachable posterior referencing feet 43. Referencing feet 43have flanges 50 which extend through and slidably engage slots 49 a and49 b. In this embodiment, proximally facing surface 48 will contact theresected planar distal surface of the femur and the posteriorreferencing feet 43 reference the posterior aspect of the femoralcondyles prior to their resection. The posterior referencing feet 43 areremovably connected to the positioner body 42 thru the attachment slots49 a and 49 b and may include a locking mechanism such as a ball detentto hold them in slots 49 a and 49 b. Further, the posterior referencingfeet 43 each have an attachment flange 50 inserted into the attachmentslots 49 a and 49 b. Flange 50 is connected to a known length connectionleg 51 and a posterior referencing arm 52. The connection leg 51 maycome in multiple lengths to allow for interoperative adjustments andtherefore allow for adjustments in the AP and internal-externalpositioning of the positioner assembly. Once the desired orientation ofthe positioner assembly is obtained, the positioner body may be used toalign the femoral four in one resection guide. This is done by drillingthrough the apertures 53 a and 53 b. FIGS. 6 a-6 c illustrate a sideview, a top view and a rear which of the posterior referencing feet 43.Both the medial and lateral referencing feet may be identical. FIG. 7further illustrates the positioner body 42.

The method of use for the positioner assembly 40 illustrated in FIGS.4-7 will now be described. The proximally facing surface 48 ofpositioner body 42 is placed on the resected distal end of the distalfemoral bone. At this point the surgeon will insert posteriorreferencing feet 43 into attachment slots 49 a and 49 b. The posteriorreferencing member 52 will contact the unresected posterior cartilage onthe right and left condyles of the distal femur and different thicknessreferencing members 52 of predetermined thicknesses (preferably in 1 mmincrements) allow for the surgeon to set alignment (anterior, posterior,and internal/external rotational i.e. axial alignment) of the femoralfour in one resection guide which thus aligns the final femoral implantby considering any cartilage wear on the posterior condyles. Given themodularity of the posterior referencing feet 43 and the provision ofdifferent length legs 51 allows the surgeon to make alignmentmodifications to align the instrument to a pre-arthritic orientationstate. Shims can also be placed between the anterior surface of the feet43 and the posterior condyles. Once proper alignment is determined, thesurgeon will drill into the bone through apertures 53 a and 53 b. Sizingof the femoral component using this instrument would be determined bytypical implant size specific four-in-one cutting blocks which relate tothe available femoral components (not shown, but available in standardknee instrument kits) that interface with the holes in the bone. Theseholes in the bone which were drilled through bores 53 a and 53 b wouldbe used to mount standard four in one cutting guides for making twoanterior and two posterior chamfer cuts.

FIG. 8 illustrates an alternate embodiment of an anatomic distal femoralresection guide alignment assembly 75. This assembly includes ananterior cortex referencing pad 76, a stylus like extension rod member77, an AP tower 13 a, a distal femoral referencing housing 14 a andadjustable pads 22 c adjusted by screws 22 b. An important aspect ofthis embodiment is the anterior cortex referencing pad 76 which has ananterior facing surface 78, a posterior surface 79 which contacts theanterior cortex of the femoral bone and fixation apertures 80 to receivefixation pins (not shown). Extension rod member 77 may be adjusted inthe proximal-distal direction by the actuation of handle 84. Lock 86 isused to lock the member 77 as specific points 88 on a holder 90. Pad 76is preferably connected to extension member 77 by a hinge joint 77 awhich forms part of attachment mechanism 81. Hinge 77 a allows forrotation of assembly 75 about a medial lateral extending axis. Further,there is an attachment mechanism 81 which allows for a pivotalconnection to the stylus like extension member 77. Similar toembodiments described above, this embodiment of the distal femoralresection guide alignment assembly 75 allows for movement of theadjustment pads 22 c in a proximal-distal direction with respect to thefemur.

The method of use for the alternate embodiment of the anatomic distalfemoral resection guide alignment assembly 75 illustrated in FIG. 8 issimilar to the methods described for the instrument in FIGS. 1-3. Theexception if the addition of the anterior cortex referencing pad 76which allows for positioning of the component at different flexionangles, such as 3-5 degrees. A distal resection cutting guide is notshown in this figure, but it can be envisioned that a distal resectioncutting guide similar to 11 having an anteriorly-posteriorly extendingplanar cutting surface can be removably connected to referencing housing14 a. Once the appropriate alignment is determined, the distal resectionguide would be pinned to the anterior aspect of the bone and a distalbone resection would be made.

FIGS. 9-11 illustrate various embodiments of an AP sizer assembly (100,100 a, 100 b). Each assembly may consist of an AP sizer body (101, 101a, 101 b) having a plurality of slots corresponding in size to availablefemoral components, calibrated sizing slots (102, 102 b) and removablyattachable posterior referencing members (103, 103 a, 103 b).

The method of use for different AP sizer assemblies (100, 100 a, 100 b),illustrated in FIGS. 9-11. Here various removably attachable posteriorreferencing spacers (103, 103 a, 103 b) may be used to compensate forany posterior cartilage wear (preferably in 1 mm increments) and animplant size for a femoral component may be determined by using a sizingstylus or sizing slots with an angle wing 99 for instance. Angle wing orblade runner plate 99 allows the surgeon to estimate the femoral implantsize.

FIG. 12 illustrates a femoral referencing tibial resection alignmentsystem 200. This instrument references the resected distal femur to setthe proximal tibial tibial resection. Alignment system 200 consists ofthe following: a trial-like femoral referencing member 201, femoralspacer elements 202, resection guide tower 203, proximal rod 204 tibialadjustment housing 205 with adjustment wheel 205 a and an adjustableslope tibial resection guide 206. The trial-like femoral referencingmember 201, further illustrated in FIGS. 13-14, consists of a proximalfacing surface 207, a distal facing surface 208, elongate peg members209, fixation apertures 210 for receiving bone pins and an extensionmember 211. The proximal surface 207 contacts the distal surface of theprepared femoral bone and the elongate peg members 209 are receivedwithin previously prepared apertures in the prepared distal surface ofthe femur. The distal surface 208 contains an attachment mechanism forengaging femoral spacer elements 202. Femoral spacer elements 202,further illustrated in FIGS. 19-20, have a distal surface 212, aproximal surface 213 and a connection member 214. Elements 202 may havevarious thicknesses between the proximal surface 213 and distal surface212. Preferably the thickness increases in 1 mm increments from 1 mm to3 mm. Extension member 211 engages the resection guide tower 203 andallows for adjustments in the AP direction. In the illustratedembodiment extension 211 slides in a hollow guide 211 a.

Further regarding the femoral referencing tibial resection alignmentsystem 200, the resection guide tower 203 may be removably orpermanently connected to the proximal rod 204. The rod 204, furtherillustrated in FIG. 15, may consist of markings 220 and thread-likefeatures or ratchet elements 221. The markings may be spaced at 3 mm.The tibial adjustment housing 205 engages with the rod 204 and may beavailable in zero (0) and three (3) degree slope embodiments. The tibialadjustment housing is further described in a Stryker owned U.S. Pat. No.7,033,361, the disclosure of which is incorporated herein by reference.The adjustable slope tibial resection guide 206 is removably attached tothe tibial adjustment housing and may consist of a proximal cuttingsurface 230, aperture 231 for receiving a navigation tracker, cross pinfixation aperture 232 and two conical holes 233. Conical holes 233 arefurther illustrated in FIGS. 16-18 and allow for tibial slopeadjustments from 0-5 degrees with respect to a transverse plane in theAP direction. Here a fixation pin would be inserted thru a conical hole233, and the tibial slope which hole 233 can be adjusted and then theadjustable tibial resection guide 206 can be fixed to the proximaltibial bone by inserting an additional fixation pin through aperture232.

Femoral referencing tibial resection alignment system 200 allows for theadjustable slope tibial resection guide 206 to be placed by referencingboth the prepared distal surface of the femoral bone and the un-resectedtibial surface. Further the system 200 allows for adjustability in theAP direction and proximal distal direction.

The method of use for the femoral referencing tibial resection alignmentsystem 200 illustrated in FIGS. 12-20 will now be described. Theproximal surface 207 of the trial-like femoral referencing member 201contacts the resected distal femoral bone. Elongate members 209interface with previously made apertures in the distal femoral bone.Also, the trial-like femoral referencing member 201 may containposterior referencing feet (not shown) to reference the posterior aspectof the distal femur. Femoral spacer elements 202 come in variousthickness, such as 1, 2 or 3 mm, and are used to simulate the femoralcondyles while compensating for any tibial cartilage wear, and thusallowing for restoration of the joint to the pre-arthritic state. Thesurgeon selects the appropriate femoral spacer elements 202 which willcontact the unresected surface of the tibial cartilage surface. Itshould be noted that proper alignment is determined with the knee inextension. Once the surgeon has properly restored the tibial/femoralstructure to a pre-arthritic state, the adjustable tibial resectionguide 206 can be pinned to the anterior surface of the tibial bone. Thetibial resection guide 206 has conical holes 233 which will allow thesurgeon to provide a posterior slope to the tibial resection surface.For example, the conical holes 233 may allow for 0-5 degrees ofposterior slope, as depicted in FIGS. 16-18.

FIG. 21 illustrates a tibial resection alignment system 300 whichconsists of a tibial adjustment member 301 may be removably attached toa tibial resection guide 302. The tibial adjustment member 301, furtherillustrated in FIGS. 22-24, preferably includes the following features:a proximal surface 303, a distal surface 304, anterior tibial cortexscribe lines 305, medial/lateral tibial scribe line 306, fixationaperture 307 and elongate connection features 320. The distance betweenthe proximal surface 303 and distal surface 304 may be a calculatedangle such as 2 degrees varus. Other such geometries can be used such tomodify the tibial slope, varus alignment, valgus alignment of anycombination. When in use, the distal surface 304 contacts the resectedproximal surface of the tibia and elongate connection pins 320 engageconnection bores in bores 308 on the tibial resection guide 302.Further, the anterior tibial cortex scribe lines 305 align with theanterior cortex of the tibial bone and the medial/lateral tibial scribelines 306 align with the respective medial/lateral tibial cortex. Thetibial resection guide 302 can be attached to the proximal tibia bone byinserting fixation pins thru apertures 332. Further, refinement cuts canbe made by utilizing the proximal resection surface 330 and anappropriate surgical saw. Also, a well-known navigation tracker may beassembled to the tibial resection guide 302 at aperture 331.

The method of use for the tibial resection alignment system 300, FIGS.21-24, will be now described. If, following a preliminary resection ofthe tibial surface, the surgeon considers that a “clean-up” oradditional cut is desired, the surgeon can attach a tibial adjustmentmember 301 to a tibial resection guide 302 and make an additional cut.Here, the tibial adjustment member 301 may have various angle referencesto allow for additional resection in varus, valgus or other alignment.

The use of instruments described above during a surgery will now bedescribed. First obtain a patient MRI of the knee. Determine the femoraldeficiency and isolate the deficiency into distal medial, distallateral, posterior medial, and posterior lateral areas based on the MRI.This is done through measuring normal cartilage and documenting wear inthe four segments (for example 2 mm wear distal medial, zero wear distallateral, and zero wear posterior medial and lateral). Alternately, thecartilage/bone loss can be assessed intraoperatively to determinecartilage thickness on the unaffected condyle. Other methods todetermine cartilage loss are described in U.S. Patent Publication No.2009/0270868.

Expose knee and slide a ‘Z’ shaped retractor along the anterior cortexof the femur proximal to the trochlea. This retractor helps determinethe flexion/extension orientation of the femoral component. Drill a ⅛″pin parallel to the Z retractor into the distal most aspect of theunaffected femoral condyle (lateral for varus knee, medial for valgusknee). Assemble the distal femoral reference housing 14 of FIG. 1 bysliding it over the pin via holes 53 a or 53 b. Set distal resection at8 mm by adjusting rack and pinion 19 and 20. The goal of the distal cutis to make a resection referencing the distal femur adjusting for thewear documented from the MRI or the intra-operative measurements. Slidethe distal femoral resection guide alignment assembly 10 until theproximal surface of the distal femoral referencing housing 14 is incontact with the unaffected condyle. Adjust the varus/valgus settinguntil the proximal surface of the distal femoral referencing housing 14is positioned parallel with the distal femur after adjusting for thewear. (For example, if there is 2 mm distal medial wear, there should bea 2 mm gap between the proximal surface of the distal femoralreferencing housing 14 and the femur on the diseased side and a 0 mm gapon the lateral side. Pin the distal resection guide 11 using 2 headlesspins through bores 17, remove all other instrumentation via connector18, optionally attach a saw blade capture element, and make the distalcut. Remove the distal cut guide 11 and assemble the rotation/sizingguide of FIG. 4 and set the rotation to 0 degrees. Set femoral rotationand determine femoral implant size using the posterior referencingtechnique described above adjusting the posterior references 43 of theguide 40 to account for any posterior wear documented on the MRI usingvarious leg elements. Drill through bores 53 a and 53 b in guide. Attacha sizing stylus as shown in FIGS. 9-11 and/or blade runner plate or wing99 and determine the femoral size, making sure the orientation of theguide has not changed using spacer 103. After sizing is complete mount astandard 4 in 1 cutting guide (not shown) using the drilled holes. Thecutting guide corresponds to one of the available femoral components.Make the anterior, posterior, posterior chamfer, and anterior chamfercuts. To verify the femoral preparation compare the four segments thatwere assessed by the MRI. Distal medial and lateral, and posteriormedial and lateral segments should be approximately 6.5 mm minus wear.If there is a large variation consider adjusting femoral preparationbefore moving on to the tibia.

Alternatively to the sizer with the leg elements the embodiment with theshims can be used to set rotation and determine femoral implant size.The difference in the procedure would only be the use of shims tocompensate for posterior wear rather than leg elements.

For tibial resection assemble the extramedullary tibiofemoral resectionguide of FIG. 12 with the 0 degree slope attachment 206. Inapproximately 90° flexion, place guide on tibia and use standardtechniques to assess the resection level of the tibia. Place the distalfemoral pegs of the distal femoral trial portion into the predrilledholes in the distal femur. To accommodate for tibial compartmental wear(varus knee-medial, valgus knee-lateral) use a corresponding distal shimon the backside of the distal trial portion of the assembly. It isrecommended that the remaining cartilage on the worn compartment bescraped off completely to better estimate the cartilage thickness to beaccounted for (usually 2 or 3 mm). Then bring the knee slowly intoextension, allowing the distal trial portion of the apparatus to sitwithin the proximal tibial compartments (both medial and lateral). Anextra medullary alignment tower and rod can be used to assess limbalignment at this stage (flexion-extension slope and varus-valgusrotation). Proximal tibial stylus is used according to standard protocolto assess and determine the resection level. The key is to have tibiapositioned against femur with this assembly in place. Pin the cuttingjig 230 onto the proximal tibia, using one headless pin in the mostcentral hole 233 available. With the patient's leg extended, attach thealignment tower and guide pin to the cutting jig and extend upwardly.Provide traction on the leg to assess the flexion/extension gapsrelative to the distal femoral resection.

The tibial cutting jig is properly oriented when it indicates a tibialresection parallel to the distal femoral resection. If the cuts are notparallel, slide spacers 202 to induce a varus or valgus angle to thecutting block until the jig and distal femoral resection are parallel.Place a second pin in the cutting guide then remove the tibial alignmentjig and resect the proximal tibia. If a tibial recut is required toadjust the varus valgus alignment the recut guide can be used. Theappropriate recut guide is used with element 301 attached to the tibialresection guide. Component 301 is seated on the resected tibia and thescribe line is aligned to the anterior tibial cortex as is themedial/lateral scribe line 306. The resection guide is then pinned tothe tibia and the cut can be made through the resection guide slot.

Referring to FIG. 25 there is shown an alternate distal femoralresection assembly which includes a distal femoral referencing housing414 having adjustable pads 422 a which can be adjusted by rotatingscrews 422. Pads 422 a engage the medial and lateral distal femoralcondyles respectively. The guide includes a tower 413 including a shaft404 which is held in the distal femoral referencing housing 414 by athumb screw 421 in the desired anterior posterior position. Anadjustment housing 412 is mounted on tower 413 via a post or screwconnection 420 in bores 415 of tower 413. The same distal femoralresection guide 11 as shown in FIG. 1 is used and is adjusted in theproximal distal direction by an adjustment screw 419 mounted in ahousing 412.

Referring to FIG. 26 there is shown an alternate embodiment of ananatomic distal femoral resection guide alignment assembly including anAP tower 13 b, a distal femoral resection housing 14 c including theadjustable pads 22 d adjustable in the manner described above to set thevarus/valgus orientation of the distal femoral cut. An anterior cortexreferencing pad 76 a is included which has a pair of pin holes 80 a.Extension of rod 77 b and the proximal-distal direction is accomplishedvia movement of handle 84 a which may be locked in position by triggerlock 86 a which engages grooves 402 in holder 90 a. Grooves 402 may bemarked in 1, 3 or 3 mm increments for reference purposes. Holder 90 a ismounted on tower 13 b via post 400 into a bore 403. The use of thealternate guides of FIGS. 25 and 26 is essentially the same as thatdescribed above.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A method for replacing a knee joint,comprising: determining a naturally occurring joint surface on a distalfemur; assessing a deficiency on the distal femur from the naturallyoccurring joint surface; selecting an offset distance between first andsecond reference surfaces of an instrument based on the deficiency;contacting the distal femur with the first and second reference surfacesto determine an orientation of the instrument and a first guide surfacerelative to the distal femur; and resecting the distal femur by guidinga cutting tool along the first guide surface to form a distal resection.2. The method of claim 1, wherein the first guide surface is connectableto the instrument such that the first guide surface is positioned apredetermined distance from the instrument.
 3. The method of claim 2,wherein the predetermined distance is based on a dimension of a femoralprosthesis.
 4. The method of claim 1, wherein the first guide surface iscoupled to the instrument such that the first guide surface is parallelto and offset from at least one of the first and second referencesurfaces.
 5. The method of claim 1, wherein: the first reference surfacecontacts the distal femur at a location of the deficiency, the secondreference surface contacts the distal femur at a location other than thelocation of the deficiency, and the offset distance compensates for thedeficiency so that the instrument is aligned with the naturallyoccurring joint surface.
 6. The method of claim 5, wherein: the locationof the deficiency is at a first condyle of the distal femur, and thesecond reference surface contacts a second condyle of the distal femur.7. The method of claim 5, wherein assessing the deficiency includesmeasuring cartilage loss at the location of the deficiency from thenaturally occurring joint surface.
 8. The method of claim 1, whereinselecting the offset distance is performed intraoperatively.
 9. Themethod of claim 1, wherein assessing the deficiency is performedintraoperatively.
 10. The method of claim 1, wherein an amount resectedfrom the distal femur is determined by a thickness of a femoralprosthesis and the deficiency.
 11. The method of claim 1, whereinselecting the offset distance includes adjusting at least one adjustablepad having one of the first or second reference surface disposedthereon.
 12. The method of claim 1, wherein the instrument includesfirst and second adjustable pads, the first reference surface isdisposed on the first adjustable pad, and the second reference surfaceis disposed on the second adjustable pad.
 13. The method of claim 1,further comprising: determining a deficiency on a tibia; mounting atibial resection assembly to the tibia, the tibial resection assemblyincluding a second guide surface and a femoral reference surface;referencing the distal resection with the femoral reference surface;adjusting the second guide surface based on the deficiency of the tibia;and resecting the tibia by guiding a cutting tool along the second guidesurface and parallel to the distal resection.
 14. The method of claim13, wherein adjusting the second guide surface includes attaching atleast one femoral spacer element to an attachment mechanism disposedopposite the femoral reference surface such that the femoral referencesurface contacts the distal resected surface and the at least onefemoral spacer element contacts an unresected surface of the tibia. 15.A method for resecting a distal femur and a tibia to receive a jointimplant, comprising: determining a distal extent of a degenerated jointsurface of the distal femur; determining an amount of degeneration at afirst region of the distal femur; determining a distal extent of apre-degenerated joint surface of the distal femur based on the distalextent of the degenerated joint surface and the amount of degeneration;contacting the distal femur in the first region with a first referencesurface of an instrument and a second region with a second referencesurface of the instrument, the first and second reference surfaces beingseparated by an offset distance based on the amount of degeneration, theoffset distance and contact of the first region with the first referencesurface and second region with the second reference surface aligns theinstrument with the pre-degenerated joint surface; and resecting thedistal femur along a resection plane a predetermined distance from andin a predetermined orientation with respect to the pre-degenerated jointsurface to form a distal resection.
 16. The method as set forth in claim15, wherein: the degenerated joint surface is defined by first andsecond condyles when at least one of the first and second condyles is ina degenerated state, and the pre-degenerated joint surface is defined bythe first and second condyles when both the first and second condylesare in a pre-degenerated state.
 17. The method as set forth in claim 15,wherein the first region is located on the first condyle and the secondregion is located on the second condyle.
 18. The method as set forth inclaim 15, wherein the instrument includes a housing having a lengthextending between lateral and medial extents of the housing, the firstand second reference surfaces are disposed at a bone facing side of thehousing between the lateral and medial extents and are offset from eachother in a direction transverse to the length of the housing.
 19. Themethod as set forth in claim 15, wherein the predetermined distance andpredetermined orientation are based on a thickness of a femoralprosthesis having a prosthetic joint surface so that when the femoralprosthesis is attached to the distal resection, the prosthetic andpre-degenerated joint surfaces coincide.
 20. The method as set forth inclaim 15, further comprising: determining a deficiency on a jointsurface of the tibia; placing a tibial resection guide having aresection guide surface adjacent a non-joint surface of the tibia;shifting a longitudinal axis of the tibia with respect to the resectionguide surface based on the deficiency of the joint surface; andresecting the tibia along the resection guide surface.
 21. A method forresecting a distal femur and a tibia to receive a joint implant,comprising: determining a first amount of degeneration of a firstcondyle and a second amount of degeneration of a second condyle;determining a relative degeneration based on a difference between thefirst and second amounts of degeneration; contacting the first condylewith a first reference surface of an instrument; contacting the secondcondyle with a second reference surface of the instrument, the first andsecond reference surfaces being separated by an offset distance based onthe relative degeneration; and resecting the distal femur apredetermined distance from the instrument based on a thickness of animplant so as to locate a joint surface of the implant in substantiallythe same location as a pre-degenerated joint surface defined by thefirst and second condyles prior to the first and second amounts ofdegeneration being formed.
 22. The method as set forth in claim 21,wherein the offset distance is substantially equal to the relativedegeneration.
 23. The method as set forth in claim 21, whereincontacting the first and second condyles aligns the instrument with thepre-degenerated joint surface.
 24. The method as set forth in claim 21,further comprising: determining a third amount of degeneration of aproximal tibia; placing a tibial resection guide having a resectionguide surface adjacent a non-joint surface of the tibia; shifting alongitudinal axis of the tibia with respect to the resection guidesurface based on the third amount of degeneration; and resecting thetibia along the resection guide surface.
 25. A method of resecting adistal femur, comprising: contacting a degenerated portion of a jointsurface of a distal femur with a first bone contact surface of aninstrument; contacting an undegenerated portion of the joint surfacewith a second bone contact surface of the instrument, the second bonecontact surface being offset from the first bone contact surface adistance based on an amount of degeneration of the joint surface at thedegenerated portion such that when the first bone contact surfacecontacts the degenerated portion and the second contact surface contactsthe undegenerated portion, the instrument is aligned with apre-degenerated joint-line of the distal femur; and resecting the distalfemur at a location parallel to the pre-degenerated joint-line.